Wireless spectrum is an expensive and valuable resource but significant portions of spectrum often go unused. The concept of cognitive radio allows wireless devices to discover and use locally available and usable spectrum for communication. The wireless device should be able to sense its environment, including its location, and then be able to alter its communication parameters, including power and carrier frequency, so as to dynamically reuse available spectrum. A key technical challenge of cognitive radio is to detect the availability of the spectrum in a robust and power efficient manner. For example, when a terminal just powers up or moves into a new area, the terminal may not have knowledge of the communication parameters or even technologies that may be currently used in the vicinity of the geographical area. The detection method has to be robust, e.g., against various uncertainties including the lack of timing and frequency synchronization. Power efficiency has great impact on the battery life of the terminals and is thus another important issue in wireless systems.
In view of the above discussion, it should be appreciated that there is a need for new and improved ways for detecting spectrum availability in a radio network.